What number is the fuse in the fuse box for the instrument gauges on a 1999 e350 van?
Look at the fuse holder cover. There it should list the amp rating for that fuse. Also the owners manual will list this. Do not use any other fuse other that the listed fuse.
There is a diagram in the owners manual (page 125). Check out
http://vehicleownersmanuals.blogspot.com/ to download it for free.